1. Field of the Invention
The present invention relates to a contact structure between a flexible cable for transmitting a signal from a control unit and a signal receiving unit for receiving the signal through said flexible cable, and a recording apparatus such as a printer, a copying machine, and a facsimile apparatus for use as an output equipment for a composite machine or a work station including a computer or a word processor which uses said contact structure.
2. Related Background Art
In a variety of electronic equipments, flexible cables having a signal line formed on a flexible substrate are widely used as means for transmitting a signal from a control unit to a functional unit (e.g., a driving circuit) from the viewpoint of easy assembly. Also, as a mechanism for connecting the flexible cable to the functional unit, a contact structure has been widely used in which a contact plane of the flexible cable is contacted (pressed) with the signal receiving unit provided on the functional unit due to its elastic stress. Such a contact structure is favorable especially in removably attaching the functional unit to an apparatus main body.
On the other hand, there is described in U.S. Pat. No. 4,706,097 a contact structure between the flexible cable and the signal receiving unit for use with an ink jet recording apparatus in which the characteristic of volume change to a biasing force of an elastic member is substantially linear. According to a publication thereof, the flexible cable has a plurality of projections to be contacted with the signal receiving unit (contact plane) of a recording head on a contact plane thereof, which are arranged in a predetermined array, while the elastic member has a plurality of protrusions formed at locations corresponding to respective projections of the flexible cable on a face thereof opposed to the flexible cable. And each protrusion is columnar, with a top end portion contacted with the projection being conical. As shown in FIG. 8, each protrusion 23 has an apex of a conical portion 23a thereof located interiorly on the back side of corresponding projection 22 on the contact plane, whereby when a recording head is mounted so that each projection 22 of the flexible cable is contacted (pressed) with the signal receiving unit 24, each conical portion 23a of the elastic member 13 is elastically deformed to press each projection 22 against a contact point of the signal receiving unit 24 with a stress of elastic deformation, thereby assuring the signal transmission.
With the above constitution, the characteristic of volume change to the biasing force of elastic member is approximately linear, so that all the projections can be pressed with an excellent pressing force.
However, the above-described contact structure between the flexible cable and the signal receiving unit had the following drawbacks because contacting top end portion of the elastic member is conically shaped.
First, owing to a constitution in which the top end portion of each protrusion is contacted and pressed interiorly against the back side of each projection, when the apex position of each protrusion and that of each projection were not coincident by virtue of tolerances, a top end of the conical portion might cling to an inner face of the projection in assembling, as shown in FIG. 9, thereby making the conical portion buckled in assembling, so that the contact pressure between the contact plane and the signal receiving unit may not often reach a predetermined value. In particular, this problem will remarkably arise when the number of contact points increases.
Second, because the characteristic of volume change to the biasing force of the elastic member is not linear, numerical forecasting to attain a desired contact pressure is difficult in designing the elastic member, thereby taking some troubles in design.